The present invention relates to an optical film possessing matt property, a film having a high transmittance, a polarizing plate using the films and a liquid crystal display device using these elements.
The present invention relates also to a polarizing plate of a high transmittance possessing matt property and an optical compensative capacity and a liquid crystal display device and a color liquid crystal display device.
The construction of a liquid crystal display device in conventional art is shown in FIG. 1. An ordinary liquid crystal display device is comprised of a backlight 11 of an edge light type on the furthest back surface and, in the order from the furthest back surface, a light introductive plate 12 for injecting light from the back light toward the surface, a scattering sheet 13 for uniformly dispersing brightness of the light, and one or plural light-tuning sheet (light tuning film) 14 having a function for condensing the uniformly dispersed light by the scattering sheet to a given direction or alternatively a function for selectively transmitting or reflecting a specific polarized light. Light passing through these films is injected to a liquid crystal cell 17 interposed between a pair of polarizing plates 15 (backside polarizing plate) and 16 (surface polarizing plate). The polarizing plate is comprised usually of three layers of a polarizing layer (polarizer) interposed by 2 sheets of a protecting film. In the figure, 18 denotes a cooled cathode fluorescent tube as light source and 19 a reflective sheet.
The light tuning film 14 and the backside polarizing plate 15 located on the side of the liquid crystal cell are especially not bonded with a binder or the like so that a slight gap exists between both. This light tuning film 14 is made of an acrylic resin, a polyester, a polycarbonate or the like, but these materials are rather larger in stretching or shrinking caused by change in temperature so that the light tuning film elongated by heating due to ambient circumstance, backlight or the like is brought into contact with the backside polarizing plate 15 to cause non-uniformity in display in circumferential areas of image. In some of the light tuning films, there exists a unique brightness non-uniformity, thus bringing about deterioration in their display quality.
JP-A (xe2x80x9cJP-Axe2x80x9d means unexamined published Japanese patent application) No. Hei. 10-240143 discloses that non-uniformity in display due to contact can be improved by imparting matt property forming concavo-convex pattern onto the surface. However, control of the concave-convex pattern was not as yet controlled so that a satisfactory improved effect has not been obtained. Moreover, the transmission rate of backlight is decreased in this method due to scattering of the concave-convex surface to incur lowering of brightness for display. As for non-uniformity in brightness of the light tuning film, the use of one more scattering film is thinkable between the light tuning film and the liquid crystal cell. As the scattering film generally has haze, the transmittance will be decreased to lower display brightness as in case of imparting matt property.
In case the matt property is imparted to a film, it is general that a hard coat layer is incorporated with particles of matt property to exhibit the matt property. This hard coat layer is also provided with a function to improve scratch-resisting property so that the hard coat layer is generally made of a rigid material such as a crosslinked binder polymer. Usually, a binder polymer is allowed to crosslink after it has formed a hard coat layer. For this, however, the binder polymer may be shrunk in the course of crosslinking reaction to permit the formation of crack in the hard coat layer. Further, as the hard coat layer shrinks as a whole, a film per se provided with the hard coat layer may undergo deformation (the generation of curl, etc.). In case such film is used as the aforesaid light tuning film, defect or strain is formed to deteriorate display quality.
In view of the foregoing, a liquid crystal display device employing a conventional optical film of matt property failed to be satisfactory in display brightness and display quality.
The display type of LCD can roughly be classified into a birefringence mode and an optical rotation mode. A super twisted nematic liquid crystal display device utilizing the birefringence mode (referred to hereinafter as STN-LCD) employs super twisted nematic liquid crystal possessing a twisted angle exceeding 90xc2x0 and steep electrooptical characteristics. Therefore, STN-LCD enables display of a large capacity due to multiplex drive. However, STN-LCD has problems such as a slow response (several hundred milliseconds) and difficulty in grade display, and is inferior as compared with a liquid crystal display characteristics using active device (such as TFT-LCD and MIM-LCD).
In TFT-LCD and MIM-LCD, a twisted nematic liquid crystal possessing a twisted angle of 90xc2x0 and a positive birefringence is used for displaying images. These are a display mode of TN-LCD which is an optical rotation mode. As this mode obtains a high responsibility (several ten milliseconds) and a high contrast, this mode is advantageous in many aspects as compared with the birefringence mode. Since TN-LCD changes display colors and display contrast according to a viewing angle of looking at the liquid crystal display device (viewing angle characteristics), it involves a problem that the device is difficult in watching as compared with CRT.
JP-A Nos. Hei. 4-229828 and Hei. 4-258923 disclose a proposal of providing a phase differential plate (optical compensative sheet) between a liquid crystal cell and a pair of polarizing plate for improving viewing angle characteristics. As the phase differential plate proposed in the aforesaid publications is a phase difference is almost 0 in the vertical direction to the liquid crystal cell, it gives no optical effect on direct front but a phase difference is realized when is tilted. A phase difference generated in an inclined direction is thereby compensated. A sheet having a negative birefringence so as to compensate a positive birefringence of a nematic liquid crystal and having an inclined optic axis is effective for such optical compensative sheet.
JP-A No. Hei. 6-75115 and EP 576304A1 disclose an optical compensative sheet having a negative birefringence and an inclined optic axis. This sheet is manufactured by stretching a polymer such as polycarbonate or polyester and has a main refractive index direction inclined to the normal line thereof. As such sheet requires an extremely complicate stretching treatment, however, it is extremely difficult to manufacture a uniform optical compensative sheet of a large area stably according to this method.
On the other hand, JP-A Nos. Hei. 3-9326 and 3-291601 disclose a method using a liquid crystalline polymer. An optical compensative sheet is thereby obtained by applying a liquid crystalline polymer onto the surface of an alignment (oriented) layer of a support. As the liquid crystalline polymer fails to show a satisfactory direction on the alignment layer, however, it is impossible to enlarge the viewing angle in all directions. JP-A No. 5-215921 discloses an optical compensative sheet (birefringent plate) comprises a support and a liquid crystalline polymeric bar-type compound having a positive birefringence. This optical compensative sheet is obtained by applying a solution of the polymeric bar-type compound onto the support and curing the compound under heating. However, the liquid crystalline polymer is devoid of birefringence so that it is unable to enlarge the viewing angle in all directions.
In JP-A No. Hei. 8-50206, there is disclosed an optical compensative sheet characterized by a layer of a negative birefringence comprised of a compound having a discotic structure unit wherein an angle between the discotic compound and a support is changed in the direction of the depth of the layer. According to the method described therein, a viewing angle viewed from contrast is extensively enlarged in all directions and deterioration of images such as yellowing viewed from an incline direction is scarcely observed. With the optical compensative sheet alone, however, a Newton ring caused by contact with the light tuning film and a non-uniformity in brightness caused by the light tuning film cannot be improved. Thus, further improvement is required.
It is an object of the present invention to provide an optical film of matt property and a film having a high transmittance and matt property capable of preventing deterioration of display grade (non-uniformity of display or brightness, etc.) without causing lowering of display brightness, and a polarizing plate (a deflecting plate) of matt property as well as a liquid crystal display device using the film.
It is another object of the present invention to provide a deflecting plate of matt property improved in the degree of lowering display brightness due to scattering and lowering of display quality due to contact and scratch as well as a liquid crystal display device.
It is still another object of the present invention to provide a liquid crystal display device possessing excellent display quality in all directions by enlarging a viewing angle of a liquid crystal display device and a color liquid crystal display device of TN mode wherein a Newton ring caused by contact with a light tuning film and non-uniformity of brightness due to the light tuning film are improved and also to provide these display devices manufactured at an economic price stably in a simple manner.
The objects of the present invention have been achieved according to the following means:
(1) An optical film having matt property utilizable for an optical film on a backlight side of a liquid crystal cell in a liquid crystal display device, comprising a hard coat layer on a transparent support, the hard coat layer containing a crosslinked polymeric binder and transparent fine particles, and the surface roughness Ra being 0.1 to 0.3 xcexcm and Rz being 1 to 3 xcexcm.
(2) An optical film having matt property utilizable for an opticl film on a backlight side of a liquid crystal cell in a liquid crystal display device, comprising a hard coat layer on a transparent support, the hard coat layer containing a crosslinked polymeric binder and transparent fine particles, PC that is the number of the transparent fine particles being 20 to 200/cm.
(3) The optical film having matt property according to the aforesaid paragraph (1), wherein PC that is the number of the transparent fine particles in the hard coat layer is 20 to 200/cm.
(4) The optical film having matt property according to any one of the aforesaid paragraphs (1)xcx9c(3), wherein the transparent fine particles are organic material.
(5) The optical film having matt property according to any one of the aforesaid paragraphs (1)xcx9c(3), wherein the transparent fine particles are organic material having a Moh""s hardness of less than 7.
(6) A polarizing plate having matt property comprising the optical film having matt property of any one of the aforesaid paragraphs (1)xcx9c(5) used for at least one of the two protective films of a polarizing layer thereof and a matted layer disposed at the opposite side of the polarizing layer.
(7) A film having a high transmittance and matt property utilizable for an optical film on a backlight side of a liquid crystal cell in a liquid crystal display device, comprising a transparent support, a hard coat layer and a low refractive index layer having a refractive index lower than that of the transparent support, the hard coat layer and the low refractive index layer being overlaid on the transparent support in the written order, the hard coat layer containing a crosslinked polymeric binder and transparent fine particles, and the surface roughness Ra being 0.1 to 0.3 xcexcm and Rz being 1 to 3 xcexcm.
(8) A film having a high transmittance and matt property utilizable for an optical film a backlight side of a liquid crystal cell in a liquid crystal display device, comprising a transparent support, a hard coat layer and a low refractive index layer having a refractive index lower than that of the transparent support, the hard coat layer and the low refractive index layer being overlaid on the transparent support in the written order, the hard coat layer containing a crosslinked polymeric binder and transparent fine particles, and PC that is the number of the transparent fine particles being 20 to 200/cm.
(9) The film having a high transmittance and matt property according to the aforesaid paragraph (7), wherein PC that is the number of the transparent fine particles in the hard coat layer is 20 to 200/cm.
(10) The film having a high transmittance and matt property according to any one of the aforesaid paragraphs (7)xcx9c(9), wherein the transparent fine particles are organic material.
(11) The film having a high transmittance and matt property according to any one of the aforesaid paragraphs (7)xcx9c(9), wherein the transparent fine particles are organic material having a Moh""s hardness of less than 7.
(12) The film having a high transmittance and matt property according to any one of the aforesaid paragraphs (7)xcx9c(11), wherein the low refractive index layer contains a fluorine-containing compound capable of being crosslinked by heat or ionizing radiation and has a refractive index of 1.45 or less and a dynamic friction coefficient of 0.2 or less.
(13) A polarizing plate having a high transmittance and matt property comprising the film having a high transmittance and matt property according to any one of the aforesaid paragraphs (7)xcx9c(12) used for at least one of the two protective films of a polarizing layer thereof and a matted layer disposed at the opposite side of the polarizing layer.
(14) A liquid crystal display device which comprises the polarizing plate having matt property according to the aforesaid paragraph (6) or the polarizing plate having a high transmittance and matt property according to the aforesaid paragraph (13).
(15) An optical film having matt property comprising a hard coat layer on a transparent support, the hard coat layer containing inorganic fine particles having been treated on the surface thereof with a silane-coupling agent, a crosslinked polymeric binder, and monodisperse transparent fine particles having an average particle diameter greater than the thickness of the hard coat layer and a particle diameter distribution of 0.2 or less in terms of a variation coefficient.
(16) The optical film having matt property according to the aforesaid paragraph (15), wherein the silane-coupling agent bound onto the surface of the inorganic fine particles is chemically bonded to the crosslinked polymeric binder.
(17) The optical film having matt property according to the aforesaid paragraph (15) or (16), wherein the silane-coupling agent used for the surface treatment comprises a compound represented by the following formula (Ia), (Ib), (Ic), (Id) or (Ie): 
wherein R1, R2, R3, R4, R5, R6 and R8 in the formulas (Ia), (Ib), (Ic), (Id) and (Ie) each independently stands for an alkyl group having 1 to 4 carbon atoms or an alkoxyalkyl group having 2 to 4 carbon atoms, R7 stands for a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, n and m each stands for 2 or 3, and p stands for 2 or 3.
(18) A polarizing plate having matt property comprising the optical film having matt property according to any one of the aforesaid paragraphs (15)xcx9c(17) used for at least one of the two protecting films of a polarizing layer thereof and a matted layer disposed at the opposite side of the polarizing layer.
(19) A liquid crystal display device using the optical film having matt property according to any one of the aforesaid paragraphs (15)xcx9c(17).
(20) A liquid crystal display device which comprises the polarizing plate according to the aforesaid paragraph (18) used as a polarizing plate on the side of backlight out of the two polarizing plates disposed on both sides of the liquid crystal cell, the polarizing plate being arranged in such manner that the matted layer is faced to the backlight side.
(21) A film having a high transmittance and matt property utilizable for an optical film comprising a transparent support, a hard coat layer and a low refractive index layer having a refractive index lower than that of the transparent support, the hard coat layer and the low refractive index layer being overlaid on the transparent support in the written order, the hard coat layer containing inorganic fine particles having been treated on the surface thereof with a silane-coupling agent, a crosslinked polymeric binder, and monodisperse transparent fine particles having an average particle diameter greater than the thickness of the hard coat layer and a particle diameter distribution of 0.2 or less in terms of a variation coefficient.
(22) The film having a high transmittance and matt property according to the aforesaid paragraph (21), wherein the silane-coupling agent bound onto the surface of the inorganic fine particles is chemically bonded to the crosslinked polymeric binder.
(23) The film having a high transmittance and matt property according to the aforesaid paragraph (21) or (22), wherein the silane-coupling agent used for the surface treatment comprises a compound represented by the following formula (Ia), (Ib), (Ic), (Id) or (Ie): 
wherein R1, R2, R3, R4, R5, R6 and R8 in the formulas (Ia), (Ib), (Ic), (Id) and (Ie) each independently stands for an alkyl group having 1 to 4 carbon atoms or an alkoxyalkyl group having 2 to 4 carbon atoms, R7 stands for a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, n and m each stands for 2 or 3, and p stands for 2 or 3.
(24) The film having a high transmittance and matt property according to any one of the aforesaid paragraphs (21)xcx9c(23), wherein the low refractive index layer contains a fluorine-containing compound capable of being crosslinked by heat or ionizing radiation and has a refractive index of 1.45 or less and a dynamic friction coefficient of 0.2 or less.
(25) A polarizing plate having a high transmittance and matt property comprising the film having a high transmittance and matt property according to any one of the aforesaid paragraphs (21)xcx9c(24) used for at least one of the two protective films of a polarizing layer thereof and a matted layer disposed at the opposite side of the polarizing layer.
(26) An optical film having matt property utilizable for an optical film on a backlight side of a liquid crystal cell in a liquid crystal display device, comprising a hard coat layer on a transparent support, the hard coat layer containing inorganic fine particles having been treated on the surface thereof with a silane-coupling agent, a crosslinked polymeric binder, and monodisperse transparent fine particles having an average particle diameter greater than the thickness of the hard coat layer and a particle diameter distribution of 0.2 or less in terms of a variation coefficient, and the surface roughness Ra being 0.1 to 0.3 xcexcm and Rz being 1 to 3 xcexcm.
(27) A film having a high transmittance and matt property utilizable for an optical film on a backlight side of a liquid crystal cell in a liquid crystal display device, comprising a transparent support, a hard coat layer and a low refractive index layer having a refractive index lower than that of the transparent support overlaid in the written order, the hard coat layer containing inorganic fine particles having been treated on the surface thereof with a silane-coupling agent, a crosslinked polymeric binder, and monodisperse transparent fine particles having an average particle diameter greater than the thickness of the hard coat layer and a particle diameter distribution of 0.2 or less in terms of a variation coefficient, and the surface roughness Ra being 0.1 to 0.3 xcexcm and Rz being 1 to 3 xcexcm.
(28) A liquid crystal display device using the film having a high transmittance and matt property according to any one of the aforesaid paragraphs (21)xcx9c(24).
(29) A liquid crystal display device which comprises the polarizing plate having a high transmittance and matt property according to the aforesaid paragraph (25) used as a polarizing plate on the side of backlight out of the two polarizing plates disposed on both sides of the liquid crystal cell, the polarizing plate being arranged in such manner that the matted layer is faced to the backlight side.
(30) A polarizing plate comprising a polarizing layer interposed between 2 transparent supports, an optical compensative layer containing an optical anisotropic layer on the surface of one of the transparent supports opposite to the polarizing layer, and a matted layer on the surface of the other transparent support opposite to the polarizing layer, the optical anisotropic layer comprised of a compound of a discotic structure unit and having a negative birefringence, a disk surface of the discotic structure unit being inclined to the surface of the transparent support, and an angle of the disk surface of the discotic structure unit with the surface of the transparent support being changed in the direction of depth of the optical anisotropic layer.
(31) The polarizing plate according to the aforesaid paragraph (30), wherein the angle is increased with increasing of distance between the discotic structure unit and the surface of the transparent support.
(32) The polarizing plate according to the aforesaid paragraph (30), wherein the optical anisotropic layer further contains cellulose ester.
(33) The polarizing plate according to the aforesaid paragraph (30), wherein the transparent support of the optical anisotropic layer side has an optically negative uniaxial property and an optic axis in the direction of normal line of the surface of the transparent support and satisfies the following condition:
20xe2x89xa6{(nx+ny)/2xe2x88x92nz}xc3x97dxe2x89xa6400
wherein nx, ny, and nz stand for main refractive indices of three orthogonal axes of the transparent support, nz stands for a main refractive index in the direction of thickness of the transparent support, and d stands for a thickness of the optical compensative layer (unit: nm).
(34) The polarizing plate according to the aforesaid paragraph (30), wherein an alignment layer is formed between the optical anisotropic layer and the transparent support.
(35) The polarizing plate according to the aforesaid paragraph (30), wherein an alignment layer comprising a cured polymer is formed between the optical anisotropic layer and the transparent support.
(36) The polarizing plate according to the aforesaid paragraph (30), wherein the optical anisotropic layer is of monodomain or forms a number of domain having a size of 0.1 xcexcm or less.
(37) The polarizing plate according to the aforesaid paragraph (30), wherein the matted layer is the hard coat layer of the optical film having matt property according to any one of the aforesaid paragraphs (1)xcx9c(5) and (15)xcx9c(17), or a lamination layer composed of the hard coat layer and the low refractive index layer of the film having a high transmittance and matt property according to any one of the aforesaid paragraphs (7)xcx9c(12) and (21)xcx9c(24).
(38) The polarizing plate according to the aforesaid paragraph (30), wherein the matted layer contains particles having a diameter of at least 1.0 xcexcm and a low refractive index layer having a refractive index of 1.45 or less is overlaid on the matted layer.
(39) The polarizing plate according to the aforesaid paragraph (38), wherein the matted layer contains therein monodisperse transparent fine particles comprising a resin having a Moh""s hardness of less than 7, an average particle diameter greater than an average thickness of a polymeric binder forming the matted layer, and a particle diameter distribution of 0.2 or less in terms of a variation coefficient.
(40) The polarizing plate according to the aforesaid paragraph (38), wherein the low refractive index layer contains a fluorine-containing compound capable of being crosslinked by heat or ionizing radiation and has a dynamic friction coefficient of 0.15 or less.
(41) The polarizing plate according to the aforesaid paragraph (38), wherein the particles in the matted layer has a Moh""s hardness of less than 7.
(42) A liquid crystal display device comprising the polarizing plate according to any one of the aforesaid paragraphs (30)xcx9c(41) used as a polarizing plate on the side of backlight out of the two polarizing plates disposed on both sides of the liquid crystal cell, the polarizing plate being arranged in such manner that the matted layer is faced to the backlight side.
(43) A color liquid crystal display device comprising a pair of substrates having transparent electrodes, pixel electrodes, and a color filter, a liquid crystal cell sealed between the substrates and comprised of a twisted nematic liquid crystal, a pair of optical compensative sheets provided on both sides of the liquid crystal cell and a pair of polarizing plates provided respectively on the optical compensative sheets, the polarizing plates according to any one of the aforesaid paragraphs (30)xcx9c(41) being used as the optical compensative sheet on the backlight side of the liquid crystal cell and the polarizing plate, the optical anisotropic layer of the polarizing plate being disposed toward the liquid crystal cell side, the optical compensative sheet comprising an optical anisotropic layer having a negative birefringence and comprised of a compound having a discotic structure unit being disposed on the display side of the liquid crystal cell, a disk surface of the discotic structure unit being inclined to the surface of a transparent support, and an angle of the disk surface of the discotic structure unit with the transparent support surface being changed in the direction of depth of the optical anisotropic layer.
(44) The color liquid crystal display device according to the aforesaid paragraph (43), wherein a anti-reflection (reflective) layer is formed on the top surface of the display side of the display side polarizing plate.
(45) The color liquid crystal display device according to the aforesaid paragraph (43), wherein a anti-glare layer is formed on the top surface of the display side of the display side polarizing plate.
(46) The color liquid crystal display device according to the aforesaid paragraph (43), wherein a anti-glare and anti-reflection layer is formed on the top surface of the display side of the display side polarizing plate.
In the aforesaid paragraphs (30)xcx9c(46), the optical anisotropic layer preferably satisfies the following conditions:
(i) An angle of a disk surface of the discotic structure unit with the surface of the transparent support is increased with the increase in distance from the surface of the support and the optical anisotropic layer varies in the angle from 5xc2x0 to 85xc2x0.
(ii) The optical anisotropic layer having an angle of a disk surface of the discotic structure unit with the surface of the transparent support the minimum value of which is within the range from 0 to 85xc2x0 (more preferably, 5xcx9c40xc2x0), while the maximum value is within the range from 5xc2x0 to 90xc2x0 (more preferably, 30xcx9c85xc2x0).
(iii) The optical anisotropic layer contains cellulose ester (more preferably cellulose acetate butylate).
(iv) The optical anisotropic layer having the minimum value in the absolute value of retardation other than zero in the direction incline from the normal line of the polarizing plate.
(v) The substrate of the liquid crystal cell has an alignment layer subjected to a rubbing treatment in one direction as well as the optical anisotropic layer is arranged in such manner that an angle of the direction in case of positively projecting the direction of the minimum value of retardation of the layer on the liquid crystal cell with the rubbing direction of the substrate of the liquid crystal cell adjacent to the layer is 90xcx9c27xc2x0.
Other and further objects, features, and advantages of the invention will appear more fully from the following description, taken in connection with the accompanying drawings.